Excessive body hair is caused by a high level of, or hypersensitivity to, the male hormone androgen. Although women do naturally have androgen in their body, the levels of the hormone are normally low. Excessive body hair can occur when levels are higher than average, stimulating the growth of hair on parts of the body typically associated with men. For men, higher than average levels of androgen can also cause excessive hair growth, though it is harder to recognize.
For women, one main culprit of excessive body hair is polycystic ovarian syndrome (PCOS). Cysts that form on the ovaries with this condition can cause hormone imbalances resulting in raised levels of androgen and excessive body hair.
Androgen levels may also be elevated due to adrenal gland disorders and side-effects of medications (such as anabolic steroids). Though it is important to understand why your hormone levels are out of balance, excessive body hair in itself is not a health concern, and can be managed through a variety of hair removal options.